This invention relates to improvements in braking apparatus and more particularly, but not by way of limitation, to an improved disc brake assembly for off-highway vehicles having very large wheels.
Extremely large off-highway vehicles are becoming widely used in many industries, such as in the mining industry, the large construction industry, and the like. The excessive size and weight of these vehicles has created many problems in the construction and operation thereof for both efficiency and safety purposes. Of course, the wheels of these vehicles are exceptionally large, usually requiring tires in excess of ten feet in diameter. It is frequently advantageous to mount at least the front wheels of the vehicle independently, and it is preferable to provide a disc brake system for each wheel, operable independently of one another. During a braking operation, it has been found that the disc generates a considerable amount of heat, and the metallic material from which the disc is constructed frequently "seizes" the elements to which it is secured, or fuses thereto, and as a consequence, it is difficult, if not impossible, to remove the disc for replacement or repair. Usually, the disc is completely destroyed during removal thereof, which is an obvious disadvantage. In order to remedy this difficulty, an annular groove is frequently provided on the opposite faces of the brake disc in order to dissipate the heat. In actual use, however, it has been found that the groove disposed inboard or on the engaging face of the disc is less effective for heat dissipation than originally thought, since it is covered by the braking surface of the stationary brake elements, and the outboard groove is so far removed from the heating area that effective heat dissipation is difficult. In addition, the driving wheels of these large vehicles are frequently powered by a wheel motor disposed within a wheel rim and the brake disc is often operably connected with the armature of the motor. Because the armature is connected to the wheel through a gear train, the brake disc is caused to rotate at a relatively high rate of speed, or a high RPM. Thus, considerable braking effort is necessary for an efficient braking operation, and the truck may be vulnerable to a brake failure due to a gear train failure.
Furthermore, during severe conditions of usage, disc brakes can get extremely hot, after which they subsequently cool between uses. In aggravated situations, this activity results in substantial expansion and contraction, and if the disc is rigidly attached at its outer periphery by bolting or such, this expansion and contraction can result in broken or warped parts.